100 Periods of work shorter than 12 hours in a row are beneficial; beginning work each evening a couple of hours later during a shift of several days of night work can be helpful (so that workers slowly adapt to the night work), but it is not very practical, although it has been used for railroad drivers. Light treatment efficacy is well demonstrated in experimental studies, with

the treated persons showing a shift in their temperature circadian rhythm that was not obtained in controls102; bright light also improves nocturnal mental performance independently of its effect Inhibitors,research,lifescience,medical on synchronization.103 Unfortunately, many work places are only dimly lit at night. Melatonin is of little utility, both in terms of improving sleep quality and mood104 (melatonin Inhibitors,research,lifescience,medical is not available on the market in some countries, while in other countries, it can be found in health food stores, in formulations of a quality that cannot be guaranteed). Hypnotics are probably more efficacious, as far as the subjective quality of sleep is considered. However, since most persons working night shifts have such a schedule during months, even years, hypnotics should not be prescribed to them if the prescriber follows the guideline recommendations Inhibitors,research,lifescience,medical to limit the prescription to a few weeks only, because of

the risk of dependence. Multimodal approaches with scheduled bright light and darkness, sunglasses, and melatonin have been Inhibitors,research,lifescience,medical proposed to improve adaptation to shift work.105 Sleep phase shift syndromes The two situations of delayed or enhanced sleep phase syndromes are Protein Tyrosine Kinase inhibitor extremes where the circadian clock is locked to earlier or later astronomical time than socially well accepted. In the sleep delay syndrome, persons prefer to go to sleep very Inhibitors,research,lifescience,medical late at night, for example after 2 or 3 am and sleep late in the morning. In the sleep advance syndrome, the opposite situation is found. These

conditions can be familial and hereditary.78,106 Subjects with the delayed sleep phase syndrome might also show a particular personality profile, with manifestations from the domains of anxiety and mood disorders, as well as hypochondriasis.107 Techniques have been proposed to treat the extreme cases of sleep phase syndromes by modification of lighting,108 of sleeping schedule, or by a progressive shift of the time to go to sleep of 2 the hours each night.109 Mood disorders It was observed more than a hundred years ago that a few mood disorder patients have regular (periodic) recurrences of depression (with or without episodes of mania). For more than 50 years, hypotheses have been proposed for the biological mechanisms of mood disorders, but none is as yet accepted. This is in contrast to the fact that many causes of depression are well recognized, such as loss and grief, endocrine disorders (Cushing’s disorder, hypothyroidism, hyperparathyroidism, etc), differences in season, and the menstrual cycle.